1. Field of the Invention
The present invention relates to an ink, and an ink-jet recording method and instruments using the ink. In particular, the present invention relates to an ink which permits highly fine and high-image quality recording or printing on non-coated paper such as paper for copying, paper for reporting, bond paper and continuous business forms, i.e., so-called plain paper, which are commonly used in offices and homes, to say nothing of coated paper specially prepared for ink-jet recording, and on cloth, an ink-jet recording method using such an ink, and a recording unit, ink-jet recording apparatus and ink cartridge containing such an ink therein.
2. Related Background Art
Inks of various compositions have been hitherto reported with respect to inks for ink-jet recording. In particular, in recent years, detailed research and development have been made from various aspects such as composition and physical properties of inks with a view toward conducting good recording or printing on plain paper such as paper for copying, paper for reporting, notepaper and letter paper, which are commonly used in offices, and on cloth.
With respect to ink-jet recording methods, those of very different systems have heretofore been reported, including a system in which charged ink droplets are continuously generated to use a part of them in recording, a system in which signals are applied to a recording head having a piezoelectric element to generate droplets of a recording liquid according to the signals, thereby conducting recording, and a system in which thermal energy according to recording signals is applied to a recording liquid in a chamber of a recording head to generate droplets of the recording liquid by the thermal energy, thereby conducting recording.
In particular, a system of a type wherein an ink is ejected by the bubbling phenomenon of the ink caused by thermal energy as described in Japanese Patent Application Laid-Open No. 54-59936 has recently attracted attention in that the high integration and high densification of nozzles can be realized with ease. However, since the system makes good use of the bubbling, which is a phenomenon different from those of other systems, more stringent conditions are required of the inks to be used.
As preferable conditions required of inks used in such a system, may be mentioned the following conditions:
(1) having good frequency responsiveness, whereby ink droplets are ejected stably at all times from minute ejection orifices without causing clogging, and in particular, having good responsiveness of bubbling to thermal energy; PA1 (2) even when allowed to stand without capping a head during the suspension of recording, being able to be stably ejected from just after the resumption of recording, namely, being unlikely to dry in the vicinity of ejection orifices and hence causing no clogging; PA1 (3) providing high-quality images free of undefined or irregular feathering and/or bleeding, in particular, on plain paper and cloth; PA1 (4) having quick fixing ability (good drying ability) on plain paper and cloth; PA1 (5) having good storage stability and being able to keep good ink performances over a long period of time, and moreover causing neither disconnection nor deposition of foreign matter on a heating head, in particular, in the case of recording by a system making good use of thermal energy; and PA1 (6) being highly safe from toxicity, inflammability and the like.
Many proposals have heretofore been made with a view toward meeting such requirements. For example, inks generally contain a high-boiling organic solvent such as glycol for the purpose of preventing drying and clogging, and the like. When such an ink has been used to conduct recording on plain paper high in sizing degree, there have been problems in that the ink does not readily penetrate into the interior of the paper and an area on which a record has been made does not dry well, so that when such an area is touched with a finger, the finger is smeared with the ink, or the unrecorded area of the paper is stained due to rub-off of the characters recorded. Besides, when printing has been conducted on a cloth with such inks, such problems that marked bleeding occurs and color depth is also low, resulting in the formation of dull images, have occurred.
Under such circumstances, in order to enhance the penetrability of an ink into the interior of the paper, Japanese Patent Application Laid-Open No. 55-29546 has proposed a method in which a great amount of a surfactant is added to the ink. In this case, however, feathering has occurred to an extremely great extent on some kind of paper. In the case where such an ink is charged into a head for ink-jet, there have been recognized such problems such as the ink receding from an orifice surface, resulting in a failure in ejection of the ink, or the whole of the orifice surface is wetted to the contrary, also resulting in failure in ejection of the ink, though it varies with the structural conditions of the head.
It has also been proposed in Japanese Patent Application Laid-Open No. 56-57862 to make the pH of an ink strongly alkaline. This method, however, involves such drawbacks that the ink is harmful when touched with fingers, and poor results may be obtained in view of both resistance to feathering and fixing ability against paper using a certain kind of size, for example, neutralized paper.
Besides the above proposals, various improvements have been attempted to date. However, there has not yet been known under the circumstances any ink which can sufficiently solve all the problems of the feathering, drying ability and clogging. It is important to design an ink having a performance with good frequency responsiveness in addition to the above properties. Such a subject is however extremely difficult to attain.